Ring diffusers are known from the prior art and as indicated in EP 1 574 667 A1, are used, for example, in gas turbines. The gas turbines usually serve for the stationary regeneration of energy or as a drive of aircraft, the ring diffuser initially mentioned often being provided at the outlet of the gas turbine compressor, referred to briefly as a compressor, in order to decelerate the air sucked in and compressed in the compressor and converge its kinetic energy content into static pressure. Normally, in this case, the compressor outlet diffuser is formed by a circular outer wall and a likewise circular inner wall arranged coaxially thereto, between which the ring-shaped diffuser duct is provided. The diffuser duct in this case diverges from the inflow-side end to the outflow-side end.
An alternative gas turbine diffuser is known, for example, from U.S. Pat. No. 5,592,820. The diffuser disclosed therein is composed of a multiplicity of tubes of square cross section which are arranged so as to lie in a circle. On the inflow side, the tubes end on an identical radius, whereas, on the outflow side, the tubes end on different radii, thus leading to a distribution of the tube ends which oscillates multiply about a circular line. With the aid of this arrangement, the air provided by the compressor is to be conducted in a comparatively simple way to different components.
In addition, a ring diffuser for a catalytic converter of an automobile is known from EP 0 410 924 A2 which on the outlet side has a casing wavy in the circumferential direction, in order to prevent flow breakaways possibly occurring at this location.
As is known, in gas turbines, the outlet of the compressor, mostly embodied in an axial type of construction, coincides with the inlet of the ring diffuser. A guide vane cascade is provided at the outlet of the compressor or directly upstream thereof. The guide vane cascade is in this case designed either as a guide vane cascade of the last compressor stage and/or as a follow-up guide wheel and, as is known, serves for untwisting the air flowing in the ring-shaped flow duct of the compressor.
Depending on the type of construction, it is known in this case for the guide vanes of the guide vane cascade to be designed so as to be free-standing. The use of free-standing guide vanes in the last compressor stage and in a follow-up guide wheel, present if appropriate, nevertheless leads, particularly in the case of relatively large radial gaps between the free-standing guide vane tips and the inner wall lying opposite them, to a phenomenon where the velocity distribution or total pressure distribution at the outlet of the compressor stage or of the follow-up guide wheel is noticeably uneven along the circumference because of the influence of the eddy flow generated by the gap. Depending on the degree to which the follow-up guide wheel or the guide vanes of the last compressor stage are deflected, the secondary flow which likewise occurs may also possibly give rise on the outer wall to a corresponding unevenness in the outlet velocity. The result of this is that, upon entry into the diffuser, the distribution of the flow magnitudes varies in the circumferential direction and is periodic with the number of follow-up guide wheel passages. This uneven distribution of the kinetic energy causes a correspondingly spatially different capacity of the flow to run counter to the relatively even static pressure gradient in the diffuser.
Instead of free-standing guide vanes, it is also known to use guide vane leaves fastened to platforms on both sides for the vane cascade. In guide vane cascades of this type, there are no radial gaps on the side of the blade leaf tips, so that less significant unequal distributions of flow magnitudes occur here.